1. Field of the Invention
The present invention relates to a gas-generating, pressure-sensitive adhesive composition. More particularly, the present invention is concerned with a gas-generating, pressure-sensitive adhesive composition comprising: a pressure-sensitive, ultraviolet irradiation-curable adhesive (A) containing a photoinitiator, wherein the adhesive (A) transmits therethrough an ultraviolet radiation; and a gas generator compound (B) which generates a gas upon irradiation thereof with an ultraviolet radiation. In the gas-generating, pressure-sensitive adhesive composition of the present invention, the gas generator compound (B) is operably combined with the pressure-sensitive, ultraviolet irradiation-curable adhesive (A), so that, in operation, when the gas-generating, pressure-sensitive adhesive composition which is adhered to an adherend is irradiated with an ultraviolet radiation, the gas generator compound (B) generates a gas and the gas effuses at an interface between the gas-generating, pressure-sensitive adhesive composition and the adherend to thereby facilitate release of the adherend from the gas-generating, pressure-sensitive adhesive composition. Therefore, in the working (e.g., grinding or cutting) of an electronic part, such as a precision electronic part, a substrate for an electronic appliance, or a semiconductor part (e.g., a semiconductor wafer), when the gas-generating, pressure-sensitive adhesive composition of the present invention is used as an adhesive for temporarily attaching the electronic part to a substratum (working platform) or the like, the following advantages can be obtained. That is, it is possible not only to attach the electronic part securely to the substratum or the like, but also to remarkably improve the releasability of the electronic part from the gas-generating, pressure-sensitive adhesive composition upon irradiation of the composition with an ultraviolet radiation (which is generally applied during the processing of the electronic part), so that, after the working (e.g., grinding or cutting) of the electronic part, the electronic part can be easily released from the gas-generating, pressure-sensitive adhesive composition without putting a high load on the electronic part. Accordingly, by the use of the gas-generating, pressure-sensitive adhesive composition of the present invention, the working of an electronic part can be efficiently conducted without causing breakage of the electronic part. The present invention is also concerned with a method for processing an electronic part, such as a precision electronic part, a substrate for an electronic appliance, or a semiconductor part (e.g., a semiconductor wafer) by the use of a specific gas-generating, pressure-sensitive adhesive reagent, such as the above-mentioned gas-generating, pressure-sensitive adhesive composition.
2. Prior Art
In recent years, there has been a growing tendency toward miniaturization of electronic parts, and a large number of electronic parts having a size of less than 1 mm×1 mm (i.e., precision electronic parts) have been produced. As examples of such precision electronic parts, there can be mentioned various types of semiconductor devices, such as a diode, a transistor, a rectifier, a thermistor, a varistor and a thyristor; various types of integrated circuits, such as an IC and an LSI; various types of capacitors, such as a ceramic capacitor, an aluminum capacitor, a mica capacitor, an organic film capacitor and a metallized organic capacitor; organic resistors; various types of crystal devices, such as a crystal oscillator and a crystal filter; and other electronic parts which are generally used, such as a connector, a coil, a transformer, a switch, a magnetic head, a polycrystalline silicon and a TFT (thin film transistor).
On the other hand, with respect to substrates for electronic appliances, there is a tendency toward development of technologies for multi-layering the substrates. Examples of such substrates include a sheet of glass or a polymer (such as a polyphenylene sulfide or a polyimide), and an electrode sheet comprising an electroconductive material, such as silver or copper, wherein precision electronic parts are mounted on the sheet to form a circuit.
Especially, with respect to integrated circuits (IC's), which are incorporated in all electronic appliances, there is a tendency toward miniaturization and improvement in performance, thereby promoting development of IC's having a very high density. For example, a multifunctional device comprising multiple layers of IC chips is currently under development. Further, with respect to semiconductor packages, the mounting of chip-size packages is becoming a standard technology.
In many cases, precision electronic parts have a fine structure or a small thickness. Therefore, during the production or processing of precision electronic parts, a substrate for the precision electronic part or the electronic part per se is temporarily attached to a substratum (working platform) using an adhesive.
For example, when an electronic part (such as a substrate for an electronic appliance) is processed, and transferred to or placed on a substrate to obtain an ultimate article, the electronic part is temporarily attached onto a temporary substratum using an adhesive tape or sheet which has a capability of temporarily but securely attaching the electronic part to the temporary substratum and a capability of releasing the electronic part after the working (e.g., grinding or cutting) of the electronic part.
For example, a multilayer substrate (e.g., a film capacitor) as a substrate for an electronic appliance can be produced as follows. A surface (a) of a substrate is attached onto a surface of an adhesive tape or sheet and, then, the opposite surface (b) of the substrate is worked. The worked surface (b) is attached onto a surface of another adhesive tape or sheet. Then, from the surface (a) of the substrate is released the adhesive tape or sheet to expose the surface (a), and the exposed surface (a) is worked, thereby obtaining a worked substrate (both surfaces of which have been worked). A plurality of such worked substrates are laminated to produce a multilayer substrate.
As seen from the above, in the production of precision electronic parts, adhesives for temporarily attaching the precision electronic parts to a temporary substratum (working platform) have come to play a greater role.
For example, when it is intended to work a precision electronic part, prior to the working thereof, the precision electronic part is securely attached onto an adhesive tape or sheet. After the working of the precision electronic part, it is necessary to release the precision electronic part from the adhesive tape or sheet. During such a working of the precision electronic part, it is required that the adhesive tape or sheet exhibit a high adhesion strength. On the other hand, when the resultant worked precision electronic part is picked up from the adhesive tape or sheet, it is required that the adhesive tape or sheet exhibit a low adhesion strength (i.e., excellent releasability).
A more illustrative explanation is made below, taking as an example the case where the precision electronic part is a semiconductor wafer. Generally, dicing of the semiconductor wafer is conducted by the so-called “direct pickup method”. Specifically, in the “direct pickup method”, the semiconductor wafer is securely attached onto an adhesive tape (dicing tape), followed by cutting the semiconductor wafer into segments using a rotary blade. Then, the resultant semiconductor wafer segments on the adhesive tape are picked up one by one and mounted on a die. On the other hand, in a grinding (backgrinding) operation conducted for thinning the semiconductor wafer having a circuit formed thereon, the adhesive tape is securely attached onto the circuit-side surface of the semiconductor wafer, and the opposite surface of the semiconductor wafer is ground. In such workings (dicing and backgrinding) of the semiconductor wafer, for preventing the semiconductor wafer from being broken or preventing the semiconductor wafer segments from scattering, it is required that the adhesive tape have a high adhesion strength. On the other hand, when the semiconductor wafer segments are picked up after the above workings, for preventing the semiconductor wafer from being broken, it is required that the adhesive tape have a low adhesion strength (i.e., excellent releasability).
Nowadays, with respect to semiconductor wafers, there is a world-wide trend toward enlargement of diameter and reduction in thickness. As a result, a large number of semiconductor wafers of today are susceptible to breakage due to external force. Therefore, it is now required to develop an adhesive tape which can suppress the load on a semiconductor during the dicing or pick-up thereof. Needless to say, it is most desired to develop an adhesive tape which exhibits absolutely no adhesion strength to a semiconductor wafer during the pickup thereof (“Setchaku (Adhesion)”, Vol. 43, No. 1, pp. 22-25, Kobunshi Kankokai Inc., Japan, 1999).
In an attempt to meet the requirement, several adhesive tapes have been proposed. For example, there has been proposed an irradiation-curable adhesive tape comprising an adhesive layer, wherein the adhesion strength of the adhesive tape attached to an adherend can be reduced by curing the adhesive layer by irradiation of the adhesive tape on the substratum with an ultraviolet radiation or an ionizing radiation (e.g., an electron radiation) (Unexamined Japanese Patent Application Laid-Open Specification No. Hei 1-272130). There has also been proposed an adhesive tape comprising a water-soluble polymer as an adhesive component, wherein the adhesive component can be dissolved-out from the adhesive tape by using hot water after the dicing, thereby reducing the adhesion strength of the adhesive tape.
However, the irradiation-curable adhesive tape, even after curing, still exhibits a high adhesion strength to the electronic part and, hence, the releasability of the electronic part from the adhesive tape is unsatisfactory.
In addition, trays conventionally used for transporting or mounting electronic parts also have a problem in that, when the electronic parts are placed on the trays, the electronic parts will move on the trays, so that the electronic parts are likely to be damaged by impact or to be influenced by static electricity. For solving this problem, Unexamined Japanese Patent Application Laid-Open Specification No. Hei 11-334785 discloses an adhesive tape for attaching an electronic part to a carrier (tray) used for transporting or mounting the electronic part. However, the releasability of an electronic part from the adhesive tape disclosed in this patent document is unsatisfactory.
As seen from the above, it has been desired to develop an adhesive composition having an excellent releasability from an electronic part.